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Forces Acting on
an Airplane in Flight - Level 3

Thrust

Thrust is the force that provides the forward
motion of the airplane through the air. There are several ways to
produce this forcejets, propellers or rockets but
they all depend on the principle of pushing air backward with the
object of causing a reaction, or thrust, in the forward
direction. The effect is the same whether the thrust is produced
by a propeller moving a large mass of air backward at a
relatively slow speed or by a jet moving a small mass of air
backward at a relatively high speed.

For jet aircraft, the means of thrust is the gas turbine
engine. The figure below shows the inlet and exhaust flows
of the turbojet. The negative thrust due to bringing the
freestream air almost to rest just ahead of the engine is called
momentum drag or ram drag. The resulting thrust is given by
following equation,

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